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#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
struct foo {
uint64_t a;
uint64_t b;
};
struct bounded_flex_t {
uint64_t count;
// NOTE: try to move this member somewhere else and you will get:
// counted_by.c:13:20: error: flexible array member not at end of struct
struct foo flex_array[] __attribute__((counted_by(count)));
};
void free_flex(struct bounded_flex_t **flex)
{
struct bounded_flex_t *ptr = *flex;
printf("Freeing a flexible array of %ld members.\n", ptr->count);
free(*flex);
}
__attribute__((noreturn)) void die(const char *const str)
{
fprintf(stderr, str);
exit(EXIT_FAILURE);
}
int main(int argc, char *argv[])
{
uint64_t len = 1;
if (argc == 2) {
len = (uint64_t) strtol(argv[1], NULL, 10);
if (!len) {
die("error: bad integer value!\n");
}
} else if (argc > 2) {
die("error: only pass one argument maximum!\n");
}
// That's a mouthful :P
struct bounded_flex_t *flex __attribute__((cleanup(free_flex))) = malloc(sizeof(struct bounded_flex_t) + (len * sizeof(struct foo)));
if (!flex) {
die("error: could not allocate memory for it");
}
// NOTE: if this is not the first thing that we do, and we use 'len' for the
// for loop below, then we will get a runtime error from the array bound
// checker. Hence, pretty much like in Rust :)
flex->count = len;
uint64_t accumulator = 0;
for (uint64_t i = 0; i < flex->count; i++) {
flex->flex_array[i] = (struct foo){ .a = accumulator, .b = accumulator + 1};
accumulator++;
}
for (uint64_t i = 0; i < flex->count; i++) {
printf("%ld: .a = %ld, .b = %ld\n", i, flex->flex_array[i].a, flex->flex_array[i].b);
}
}
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